Ceramic dielectric comprising calcium titanosilicate

ABSTRACT

Dielectric ceramics having a high dielectric constant, an extremely low dissipation factor, and a controlled temperature coefficient of dielectric constant between +800 and -1,000ppm/* C consists, according to this invention, of three phases composed essentially of, Mol percent calciumtitanosilicate10 about 99.5strontium titanate0.5 about 30titanium dioxideremainder.

United States Patent Taki et al. [4 1 July 11, 1972 [54] CERAMIC DIELECTRIC COMPRISING [56] References Cited CALCIUM TITANOSILICATE UNITED STATES PATENTS 1 Inventors: Hiromitsu Tflki; n Hayakawa, both 2,220,774 11/1940 Navias ..106/39 R of Osaka; Kaneomi g Ky all of 3,069,276 12/1962 Domanski.. Japan 2,277,734 3/ I942 Wainer ..106/46 FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee: Matsushita Electric Industrial Co., Ltd.,

Kadoma Osaka, Japan 1,029,539 5/1966 Great Britain ..l06/39 R [22] Filed: Aug. 6, 1970 OTHER PUBLICATIONS [2]] Appl. No.: 61,745 De Vries, R. C. et al., Phase Equilibrium in the System CaO-TiO SiO in T. Amer. Cer. Soc, 38, 1955 pp. 158- 161. Related US. Application Data [63] Continuation-impart of Ser. No. 682,506, Nov. 13, 'f 'f 1967 abandoned. Asszstant Exammer-W. R. Satterfield Attorney-Wenderoth, Lind & Ponack 30 Foreign Application Priority Data [57] ABSTRACT Dielectric ceramics having a high dielectric constant, an ex- March 27, 1967 Japan ..42/19747 namely low dissipation factor, and a controlled temperature coefficient of dielectric constant between +800 and [52] US. Cl. ..252/63.5, 106/39 R, 252/520, 1, pp /o C consists, according to this invention, of three 317/258 phases composed essentially of, [51 Cl- Mol percent [58] Field of Search 106/39 R, 46; 252/63.5, 520;. calciumtitanosilicate 0 99 5 317/258 strontium titanate 0.5 30

titanium dio tide remainder.

3 Claims, 2 Drawing Figures CERAMIC DIELECTRIC COMPRISING CALCIUM TITANOSILICATE This application is a continuation in part of applicants abandoned application Ser. No. 682,506, filed Nov. 13, 1967, and assigned to the same assignee as the present invention.

This invention relates to novel ceramic materials for ceramic capacitors operating at a high frequency and more particularly to dielectric ceramic compositions comprising calcium titanosilicate, titanium dioxide, and strontium titanate.

The electronic industry has recently required dielectric materials suitable for making temperature compensated capacitors operating at high frequency, for example in a megaherz range of 1-30 Ml-iz. It is important for making such capacitors that dielectric materials have a high dielectric constant, a low dissipation factor, and controlled temperature coefficient of dielectric constant.

Polycrystalline ceramics such as titanium dioxide, magnesium titanate, calcium titanate, strontium titanate, and calcium titanosilicate are well known materials adapted for temperature compensated capacitors. However, conventional dielectric ceramic are usually bound up with a drawback that when these materials are improved so as to exhibit the temperature coefficient of dielectric constant of nearly zero value, the dielectric constant is lowered, and are not. suitable for use in high dielectric constant-temperature compensated capacitors.

Titanium dioxide is well known dielectric material with a temperature coefficient of dielectric constant of about 750 ppml C, a dielectric constant of 90-108, and dissipation factor at 1 MHz of about 0.0003. Strontium titanate has a temperature coefiicient of about 4,600 ppm/ C, a dielectric constant of 280 and dissipation factor of 1 MHz of 0.0005. Calcium titanosilicate has a temperature coefficient of about +1,200 ppml C, a dielectric constant of 30-45, and dissipation factor at 1 MHz of about 0.0005.

In addition, the electronics art has recently tended toward the miniaturization and the molding of circuits and has required dielectric materials having a high breakdown voltage for the production of thin film capacitors. Previous dielectrics with similar characteristics has a lower breakdown voltage for use in thin film capacitors.

Accordingly, a principal object of the present invention is to provide novel dielectric materials in the form of ceramics having dielectric constants much higher than those of the conventional dielectric ceramics.

A further object of the present invention is to provide dielectric ceramics characterized by high dielectric constant, low dissipation factor, high breakdown voltage, and controlled linear temperature coefficient of dielectric constant within a wide range from approximately --1 ,000 to +800 ppm/ C.

These and other objects of this invention will become apparent upon consideration of the following detailed description taken together with accompanying drawings in which:

FIG. 1 is a graph of the dielectric material in accordance with the present invention illustrating the variation of dielectric constant and dissipation factor with temperature.

F 16. 2 shows, for the dielectric material in accordance with the present invention, the variation of dielectric constant and dissipation factor with frequency at 20 C.

in accordance with the present invention, it has been discovered that ceramic materials in a composition consisting essentially of -99.5 mol percent of calcium titanosilicate (Ca'liSiO 0.5-30 mol percent of strontium titanate (Sr- TiO and remainder of titanium dioxide (TiO,) have a high dielectric constant, a low dissipation factor, a high breakdown position proportions and fired in accordance with a scheduleset forth hereinafter for production of a tired ceramic body.

The raw materials are a reagent-grade calcium carbonate (CaCO a pure grade strontium carbonate (SrCO a high purity silica (SiO and a commercially pure grade titanium dioxide (TiO Any compound which is converted to the corresponding calcium oxide or strontium oxide upon firing can be used as raw material. Batches are ball milled with water for intimate mixing and then dried. Usually, they are pressed loosely into pellet form and calcined in a covered alumina crucible. Strontium titanate (SrTiO is produced by calcining strontium carbonate-titanium dioxide mixture at 1,100" C for 2 hours and calcium titanosilicate (CaTiSiO is produced by calcining calcium carbonate-titanium dioxide-silicon dioxide mixture at l,050 for 2 hours.

The starting materials are thoroughly mixed with water in a ball mill using agate pebbles. The resultant mixture is dried at 150 C. The resultant powder is admixed with an emulsion of binding agents such as polyvinyl alcohol (PVA) in a proportion of 100 grams of the powder to 8 cc of 6 percent aqueous emulsion of PVA. The powder is pressed at 750 l(g/cm into the form of discs. These discs are fired at a temperature ranging from l,150to 1,320 C for 2 hours. A temperature rising rate of 5 C per minute is maintained. After soaking at l,150- to 1,320 C for 2 hours, they are cooled at furnace power off.

Silver paste is fired on the disc surfaces to form electrodes in per se conventional manner.

The dielectric constant and dissipation factor were measured with a conventional capacitance bridge at 20 C and 50 percent rh, at a frequency of 1 MHz and 10 MHz, and with 0.10 V/cm peak to peak. The temperature coefficient of dielectric constant is calculated from the temperature variation of the dielectric constant over a temperature range of 30 to C and expressed with a unit of parts per million per C, (p.p.m/ C). The breakdown voltage test is done in silicon oil at C by applying a d.c. field for 30 minutes.

The foregoing procedure is followed by each of the compositions hereinafter enumerated.

Referring to Table l, variation in the dielectric constant and dissipation factor at 20 C, temperature coefficient of dielectric constant and breakdown voltage of dielectric elements employing the ceramic materials in accordance with the present invention are shown as a function of the compositions. After firing, the ceramic specimens are analyzed with a Geiger-counter type X-ray diffractionmeter using CuK radiation. It has been discovered according to the present invention that ceramic materials in a composition shown in Table 2 have high dielectric constant and low dissipation factor and are suitable for use in temperature compensated capacitors. These ceramic materials exist in two phases of sphene structure (CaTiSiO and perovskite structure (SrTiO It is possible for these ceramic materials to realize a wide range of temperature coefficient of +800 to l,000 ppml C without impairing dielectric constant and dissipation factor.

TABLE i-(ontinued Electrical properties Dissipation Break Composition (moi iaetor (X10 down percent) Dielectric voltconstent 1 10 Temperaage (kv./ CflTlSlOfi SIT103 at 1 mHz mI-Iz mHz turo 1 mm.)

l Coeiiicient of dielectric constant in p.p.m./ C.(30+85 0.).

Sample is [or comparison.

TABLE 2 The ceramic materials of Table 3 give three phases of sphene structure (CaTiSiO rutile structure (TiO and perovskite structure (SrTiO The dielectric constant of these ceramic 20 'materials ranges from to i64 while the dissipation factor 25 Table 4 shows that the compositions can exhibit an-excellent dielectric activity. As apparent from Table 5 for example,

an increase in the amount of SrTiO makes the dielectric constant higher.

The ceramic materials according to the present invention have dielectric constant which varies linearly with temperature in the temperature range of -30 to +85 C. FIG. 1 shows typical temperature dependence of capacitance of sample N0. 16 in Table 4.

FIG. 2 shows the variationof dielectric constant and dis- 35 sipation factor with a variation in frequency from i KHz to about 50 MHz at 20 C. The used ceramic material is sample No. 16 in Table 4. The dielectric constant of this ceramic Sr'iiO and more than 99.5 mol percent of CaTiSiO there appears only, a single phase of sphene structure. The fired body existing in such single phase shows a low dielectric constant. The compositions comprising more than 30 mol percent of Sr- 30 TiO and less than moi percent of CaTiSiO result in a high dissipation factor.

it is further discovered according to the present invention that ceramic materials in a composition shown by Table 3 exhibit a higher dielectric constant than those of the ceramic materials shown in Table 2.

B TA LE 3 material is constant over this frequency range whereas the dis- Preferable moi percent -r s o 5 sipation factor starts increasing from about 30 MHz. 0.5-89.5 40 As shown in Tables 1, 3 and 4, the ceramic materials ac- 05-30 cording to the present invention can make it possible to pro- TABLE 4 Composition (moi percent) Electrical properties Dissipation Break Dielectric factor (X10 Tomdown constant pcravoltage (Ja'IlSiOr. T102 Sr'IiO; at 1 ll'lHZ 1 mllz 10111112 turo (kv./mm.)

1 Coefficient oi dielectric constant in p.p.m./C(-30+85 0.).

TABLE 5 Composition (moi percent) Electrical properties Dissipation Break Dielectric factor (X10- 'Iemdown constant peravoltage CaTiSiO T102 SrTiO; at 1 mHz 1 mHz 10 mHz ture 1 (kw/mm.)

Number:

25 40 60 0 64 6.0 6. 5 180 35. 6 26" 31. 95 60 0. 05 67. 1 5. 7 6. 4 195 36. 8 27* 39. 9 60 0. 1 70 5. 0 5. 3 -2iO 37. 0 8 39. 5 60 0. 5 101 3. 2 3. 6 42. 4 29 35 60 5 108. 6 2. 8 3. 7 48. 6 30 30 60 10 140. 4 3. 3 4. 0 250 48. 5 31 20 60 20 152. 7 4 4. 5 -650 40. 7 32 10 60 30 164. 2 4. 9 5. 0 1, 000 38. 8 33" 8 60 32 181 7.0 12v 4 1, 720 26. 8

1 Coeiiicient of dielectric constant in p.p.m./ (1. (30+ii5 (3.). Sample is for comparison.

vide a wide variation in the temperature coefficient without impaining dielectric constant and dissipation factor. This is due to the fact that the ceramic materials exist in two or three phases.

What is claimed is:

l. A fired ceramic dielectric composition having a dielectric constant of 50 to 164, a dissipation factor below 5 X and a linear temperature coefficient of dielectric constant of +800 to --l ,000 parts per million per C in the temperature range of 30to 85 C, said composition consisting essentially of mixed phases of 10 to 99.5 mole percent of calcium titanosilicate, 0.5 to 30 mole percent of strontium titanate and the remainder being titanium dioxide.

2. A fired ceramic dielectric composition having a dielectric constant of 50 to 164, a dissipation factor below 5 X 10-, and

a linear temperature coefiicient of dielectric constant of +800 to l,000 parts per million per C in the temperature range of 30 to C, said composition consisting essentially of two phases of 70 to 99.5 mole percent of calcium titanosilicate and 

2. A fired ceramic dielectric composition having a dielectric constant of 50 to 164, a dissipation factor below 5 X 10 4, and a linear temperature coefficient of dielectric constant of +800 to -1,000 parts per million per * C in the temperature range of -30* to +85* C, said composition consisting essentially of two phases of 70 to 99.5 mole percent of calcium titanosilicate and 0.5 to 30 mole percent of strontium titanate.
 3. A fired ceramic dielectric composition having a dielectric constant of 50 to 164, a dissipation factor below 5 X 10 4, and a linear temperature coefficient of dielectric constant of +800 to -1,000 parts per million per * C in the temperature range of -30* to +85* C, said composition consisting essentially of three phases of 10 to 69.5 mole percent of calcium titanosilicate, 0.5 to 89.5 mole percent of titanium dioxide and 0.5 to 30 mole percent of strontium titanate. 